Problem 41 - A Complete Resource Book in Chemistry for JEE Main

Question

\(\mathrm{H}_{3} \mathrm{PO}_{2}\) is the molecular formula of an acid of phosphorus. Its name and basicity respectively are (a) hypophosphoric acid and two (b) hypophosphorus acid and one (c) hypophosphorus acid and two (d) phosphorus acid and two

Step-by-Step Solution

Answer

The correct choice is (b) hypophosphorus acid and one.

Step 1: Identify the Acid

The acid with the molecular formula \( \mathrm{H}_3\mathrm{PO}_2 \) is known as hypophosphorus acid. In this formula, the name 'hypophosphorous' refers specifically to this type of phosphorus compound.

Step 2: Count Ionizable Hydrogens

To determine the basicity of the acid, we count the ionizable hydrogen atoms. In hypophosphorus acid, only one hydrogen atom is ionizable, which is connected to the oxygen atom. The two remaining hydrogen atoms are attached directly to phosphorus and are therefore not ionizable.

Step 3: Determine Basicity

Based on our analysis, hypophosphorus acid has a basicity of one, because it can donate just one hydrogen ion (\(\mathrm{H}^+\)). Basicity refers to the number of protons an acid can donate, which is one in this case.

Step 4: Select Correct Answer

With hypophosphorus acid identified as the compound, and knowing its basicity is one, the correct choice from the given options is (b) hypophosphorus acid and one.

Key Concepts

Basicity in Acids

Basicity in acids refers to the number of hydrogen ions (\( \mathrm{H}^{+} \)) an acid can donate in a chemical reaction. In simpler terms, it’s about how many ionizable hydrogen atoms the acid contains. Not all hydrogen atoms in an acid are ionizable. Whether a hydrogen atom is ionizable or not depends on its position within the molecule.
In the case of hypophosphorous acid (\( \mathrm{H}_3\mathrm{PO}_2 \)), only one hydrogen atom is ionizable. This means hypophosphorous acid can release just one hydrogen ion when it reacts. This is because two of the hydrogen atoms are attached directly to the phosphorus atom, which makes them non-ionizable. As a result, hypophosphorous acid is a monoprotic acid, meaning its basicity is one, indicating it can donate only one proton.

• Monoprotic acids: donate 1 proton (basicity = 1)
• Diprotic acids: donate 2 protons (basicity = 2)
• Triprotic acids: donate 3 protons (basicity = 3)

It's important to identify the ionizable hydrogens to correct predict an acid's basicity.

Molecular Formula Analysis

Molecular formula analysis involves interpreting a chemical compound's formula to understand its composition. For hypophosphorous acid (\( \mathrm{H}_3\mathrm{PO}_2 \)), it consists of three hydrogen atoms, one phosphorus atom, and two oxygen atoms. These atoms are arranged in a unique structure which defines the properties and behavior of the acid.
This formula analysis helps identify which hydrogen atoms are ionizable. Typically, hydrogen atoms bonded to oxygen have a higher likelihood of being ionizable due to the polarity of the \( \mathrm{O-H} \) bond. In hypophosphorous acid, the two hydrogen atoms attached to phosphorus are not readily ionizable, which affects the basicity of the acid.
Understanding the arrangement of atoms assists in determining chemical properties and the behavior of a compound in a chemical reaction. For instance, the structure of \( \mathrm{H}_3\mathrm{PO}_2 \) determines that only one \( \mathrm{H}^+ \) can be donated. Thus, chemical formulas provide vital clues about the reactivity and functionality of the compound.

Acid Naming Conventions

Acid naming conventions are standardized rules used to name acids based on their composition. When you come across an acid formula like \( \mathrm{H}_3\mathrm{PO}_2 \), knowing its name is essential for understanding its characteristics and behavior.
The name "hypophosphorous acid" is derived from the presence of the phosphorus atom and the specific conditions of the acids’ oxyanions (an ion containing oxygen). In naming acids, prefixes like "hypo-" and suffixes like "-ous" and "-ic" are used to indicate different oxidation states and numbers of oxygen atoms. "Hypo-" implies a lower number of oxygen atoms compared to its counterparts, like hypophosphoric acid.
This systematic approach helps in easily differentiating various compounds that have similar elements but different structures or properties.

• Hypo- means fewer oxygen atoms.
• -ous relates to a lower oxidation state compared to -ic.
• Phosphorous refers to the central element in the compound.

Mastering these naming conventions is crucial for the effective communication and study of chemistry.